1. Field of the Invention
The present invention is related to a seal device for a rolling bearing, specifically a seal device installed in a miniature bearing for rotation support in a hard disc drive apparatus (HDD), a video tape recorder (VTR) etc.
2. Description of the Related Art
The rotation support section in the devices such as an HDD or VTR is made up of rolling bearings which are constructed as shown in FIG. 20 to have an outer race 1 and an inner race 3. The outer race 1 has an outer raceway 2 formed around the inner peripheral surface at its axial center portion, and the inner race 3 has an inner raceway 4 formed around the outer peripheral surface at its axial center portion. There are a plurality of rolling elements 5 located between the outer raceway 2 and the inner raceway 4 that rotate freely, making it possible for the outer race 1 to rotate freely with respect to the inner race 3. These rolling elements 5 are held by a retainer 6 so that they are able to rotate freely.
The "outer race" and "inner race" are also referred to as "outer ring" and "inner ring", respectively. And, the "outer raceway" and "inner raceway" are also referred to as "outer ring raceway" and "inner ring raceway".
The rolling bearing, constructed as described above to form the rotation support section of the device such as an HDD or VTR, is filled with grease in the internal section where the rolling elements 5 are located between the outer raceway 2 and the inner raceway 4 in order to lubricate the rolling elements 5, the outer raceway 2 and inner raceway 4. Accordingly, for the rolling bearing, it is necessary to install a sealing device in order to prevent the grease from leaking out, and to separate the internal section of the rolling bearing from the outside. Accordingly, there is a shield groove 8 that is formed around the edge of the inner peripheral surface of the outer race 1.
Various kinds of such sealing devices have been known. FIGS. 21 and 22 show the sealing device that has generally been used and that has been disclosed in Japanese Utility Model First Publications KOKAI S54-68048, S58-112773, and H2-92117, and Japanese Patent First Publication KOKAI No. S62-167926.
In the case of this well known sealing device, a shield plate 7 (FIG. 22) is formed into an annular shape from sheet metal and its outer edge is caulked or crimped into the shield groove 8 as shown in FIG. 22. In other words, as shown in FIG. 21, a blank plate 9 of the sheet metal is formed beforehand with a bent section 10 on its outer peripheral edge, so that it has a smaller diameter. And this blank plate 9 is located on the inside of the shield groove 8, so that the bent section 10 is pressed against the stepped section 11 which partly defines the inside of the shield groove 8. As a result, the bent section 10 is deformed plastically in the radially outward direction, and as shown in FIG. 22, so as to be fitted into the shield groove 8. Accordingly, the diameter of the blank plate 9 is enlarged, so that the outer peripheral edge of the shield plate 7 becomes fixed in the shield groove 8.
FIG. 23 shows the sealing device that is described in Japanese Utility Model First Publication KOKAI No. S49-114350. In the case of the sealing device described in this disclosure, several attachment protrusions 13 are formed around the outer peripheral surface of the cylindrical section around the radially outer edge of the shield plate 7a. By fitting these attachment protrusions 13 to the edge or wall portion of the shield groove 8 which is formed around the end of the internal peripheral surface of the outer race 1, the shield plate 7a is supported by the inside of the outer race 1.
FIG. 24 shows the sealing device that is described in Japanese Utility Model Publication KOKOKU No. H5-16411. In the case of the sealing device described in this disclosure, the shield plate 7b is made of a sheet metal and a bent section 14 is formed on the radially outside edge of the shield plate 7b so that it bends toward the outside (the side opposite from where the rolling elements are located, or the right side in FIG. 24). By elastically fitting the bent section 14 into the shield groove 8, which is formed around the end of the inner surface of the outer race 1, the shield plate 7b is supported on the inside of the outer race 1.
Furthermore, FIG. 25 shows the sealing device that is described in U.S. Pat. No. 4,183,592. In the case of the sealing device disclosed in this patent, a tapered surface 15 that becomes smaller toward the opening end is formed on both ends of the inner peripheral surface of the outer race 1. As the outside edge of the shield plate 7c is elastically pressed toward this tapered surface, the shield plate 7c is supported on the inside of the outer race 1.
The prior art sealing devices for a rolling bearing described above have problems that should be solved, as described below.
First, in the case of the construction of the first example shown in FIGS. 21 and 22, not only does it increase the manufacturing cost, but it causes deformation of the outer race 1.
In other words, in order to support and fix the shield plate 7 on the inside of the outer race 1, it is necessary to perform a plastic deformation process (crimping) for the bent section 10. As a result the work of attaching the shield plate 7 becomes very troublesome, and together with requiring complicated equipment for performing the crimping work, it causes an increase in the cost of the rolling bearing with sealing device.
Moreover, as the aforementioned bent section 10 is plastically deformed, the bent section 10 strongly presses outward in the radial direction against the part of the outer race 1 where the shield groove 8 is formed. As a result, this part of the outer race 1 deforms elastically in the direction where the diameter becomes large. The amount of deformation caused by this elastic deformation is uneven around in the circumferential direction, causing unbalance in the outer race 1 or minute undulation in the surface of the outer raceway 2. Accordingly, if the outer race 1 or the inner race 3 of the rolling bearing rotates at high speed, it is easy for harmful vibrations to occur due to unbalanced rotation or due to the minute undulation in the surface of the outer raceway 2. Especially in recent years, as HDD devices are made more compact, the thickness of the outer race 1 becomes smaller, and problems due to elastic deformation as described above begin to be more common.
In the construction of the second and fourth examples shown in FIG. 23 and FIG. 25, the outer peripheral face of the cylindrical section 12 (second example) or the outer peripheral edge of the shield plate 7c (fourth example) strongly presses outward in the radial direction the part of the outer race 1 where the shield groove 8 or the tapered surface 15 is formed. Therefore, this part of the outer race 1 deforms elastically in the direction where the diameter becomes larger, making it easy for harmful vibrations to occur.
Furthermore, in the third example shown in FIG. 24, the elastic deformation of the outer race 1 is relatively small, however deformations as before still remain. As a result, the occurrence of defective products due to harmful vibrations increases to a level that cannot be ignored. In other words, in the construction of the third example, the bent section 14 elastically presses against the inside surface of the shield groove 8 all the way around the circumference. The elastic restoration force per unit length of the bent section 14 is small, however as it presses all the way around the inside surface of the shield groove 8, the overall force applied to the outer race 1 from the shield groove 8 is large enough that it cannot be ignored, and it causes the outer race 1 to be elastically deformed. It is impossible to avoid unevenness caused by the elastic restoration force of the bent section 14, and thus part of the outer race 1 deforms elastically in the direction where the diameter becomes large, making it easy for harmful vibrations to occur.
In Japanese Utility Model Publication KOKOKU No. H5-16411, which describes the construction shown in FIG. 24, by forming an a crown shaped or arc-shaped surface around the outer peripheral surface on the end of the outer race 1, the elastic deformation does not cause vibration even when the end of the outer race 1 is elastically deformed due to the elastic restoration force of the bent section 14. However, the work involved in manufacturing this arc-shaped surface is very troublesome, thus increases the cost for manufacturing the rolling bearing with sealing device. Moreover, it is thought that when the outer race 1 rotates at high speed, harmful vibrations occur due to the unevenness of the centrifugal moment caused by the elastic deformation.
In respect to this, it is thought that the outer peripheral edges of shield plates 7, 7a, 7b and 7c should not be pressed against the inside surface of the shield groove 8 of the outer race 1, and that the outer peripheral edges of these shield plates 7, 7a, 7b, and 7c, should be simply be attached to the shield groove 8 so that it does not come out. If the outer peripheral edge is not pressed against the inside surface of the shield groove 8, the outer race 1 is not elastically deformed, and thus it is possible to prevent the occurrence of vibrations caused by the elastic deformation.
However, with this kind of construction, since the shield plates 7, 7a, 7b and 7c may rotate relative to the outer race 1, and thus as the outer peripheral edge of the shield plates 7, 7a, 7b, and 7c comes in contact with the inside surface of the shield groove 8, it is easy for this area of contact to wear out. Wear of the area of contact causes vibration to occur due to the shakiness of the shield plates 7, 7a, 7b, and 7c, and it causes vibration to occur due to worn particles becoming attached to the rolling surface of the rolling elements 5, and therefore is not desirable.